Its regular white colored pvc, it does seem thin though. What should I use instead?

No, its pvc which I stated in the original post.

So sewer pipe is ok for combustion? Its solid core by the way.

Yeah, thats why i'm not using it and asking you people(s) what to use.

Hello everyone, I have a problem with fittings for a pvc pipe. I'm using pvc 4" sewer pipe (not sure if its safe and it doesn't fit) and it won't fit a 4" to 2" reducer or a 4" female adapter, do I need a fitting to make it fit or do I need different a pipe?